Scroll compressors have become very popular in many applications. They can be found in low temperature refrigeration systems, air-conditioning systems and specialty refrigeration systems. Scroll compressors are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning and heat pump applications due primarily to their capability for extremely efficient operation. Despite the variations in application or use, the fundamental function of the compressor is unchanged. It compresses refrigerant vapor for condensing. Heat can then be removed from the condensed vapor and the vapor then used as a cooling source.
A typical scroll compressor is comprised of three basic components. There are two mating scroll elements and an electric single-phase or three-phase motor that drives the orbiting motion of one of the scroll elements for compression of gases. Generally, these machines incorporate a pair of intermeshed spiral wraps, one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port toward a center discharge port. An electric motor is provided which operates to drive the orbiting scroll member via a suitable drive shaft.
Because scroll compressors depend upon a seal created between opposed flank surfaces of the wraps to define successive chambers for compression, suction and discharge valves are generally not required. However, when such compressors are shut down, either intentionally as a result of the demand being satisfied, or unintentionally as a result of power interruption, there is a potential for the pressurized chambers and/or backflow of compressed gas from the discharge chamber to effect a reverse orbital movement of the orbiting scroll member and associated drive shaft.
When there is a brief interruption of electric power on a single-phase model, the electric motor stops. When this happens, pockets of high pressure gas can get trapped between the scroll elements and can drive the scroll parts to rotate in the opposite or backward direction for a fraction of a second as the high pressure is relieved from the high pressure side to the low pressure side of the refrigeration circuit. If the electric power is resumed during this process, the compressor's motor will aid the backward rotation and result in a continuous backward operation. Because the compression of gases only occurs in the proper rotation, the backward motion effectively shuts down the movement of gases in the system. The associated equipment therefore malfunctions.
Since the brief power interruption could be as short as approximately twenty milliseconds, the detection of such a power change for prevention of backward operation is not always successful. This reverse movement often generates objectionable noise or rumble and possible damage.
Further, in machines employing a single phase drive motor, it is possible for the compressor to begin running in the reverse direction should a momentary power failure be experienced. This reverse operation may result in overheating of the compressor and/or other damage to the apparatus. Additionally, in some situations, such as a blocked condenser fan, it is possible for the discharge pressure to increase sufficiently to stall the drive motor and effect a reverse rotation thereof. As the orbiting scroll orbits in the reverse direction, the discharge pressure will decrease to a point where the motor again is able to overcome this pressure head and orbit the scroll member in the “forward” direction. However, the discharge pressure will now increase to a point where the cycle is repeated. Such cycling may also result in damage to the compressor and/or associated apparatus.
A need therefore exists for a mechanism for disabling operation of a scroll compressor during back pressure conditions to prevent backward operation of the compressor.